Freelance writing on Instructor visa

EDIT: I've just read about applying for 'Comprehensive Permission', which requires the application form only. Does anyone on an Instructor or other work visa have experience getting this type of permission?

I'm hoping to do some freelance writing for various outlets, most based in Japan, but I know this isn't within the remit of my Instructor visa. I want to apply for special permissions, and have looked into how to do this, but since the application process requires a contract from the side employer, and contracts don't apply to freelancing, will this be possible? Can I submit the application and say I will be working freelance?

Previously I had special permissions for doing side tutoring with a private company. If I got started this work again, would I also be allowed to do freelance writing under those special permissions?

If anyone has experience with something similar, please let me know. Thanks!